Field of the Invention
The invention relates to an electronic component, in particular to thin QFPs, in which a standardized lead frame and an integrated circuit are used and embedded in a casting or molding compound.
Surface mounted electronic components, also called SMD components, are usually embedded in a housing made of a plastic molding compound, from which electronic terminals are led out. Depending on the number of terminals required, these housings correspond to a standard having defined dimensions to enable standardized production and automatic component-mounting of circuit boards. The dimensions of these housings are defined in German and International Standards. The lead frames, which are used for embedding the electrical terminals in an exactly positioned manner, are likewise standardized. An island is provided in the center of a lead frame and an integrated circuit is fixed on the island. A lead frame and an integrated circuit are then encapsulated together by molding them in a housing made of a molding compound. Stresses occur on account of the different expansion coefficients of the iron/nickel alloy usually used for the lead frame, of the silicon chip forming the integrated circuit, and of the molding compound of the housing. The occurrence of reaction shrinkage of the molding compound creates stresses as well. Consequently, diagonal housing warpage of up to 100 μm occurs particularly in the case of large flat housings (thin QFPs, also called TQFPs).
Attempts are made to prevent this housing flexure or warpage by using special island structures. In these cases, holes or slots are made in the islands, which are arranged centrally in the lead frames. Alternatively, the islands are undercut or furrows are etched into the islands. The use of copper lead frames has also already been attempted in order to minimize the housing warpage. However, all of these solutions require either new or changed mounting processes, or they can be implemented only with etched lead frames, not with stamped lead frames, or they lead to a reduction in the rigidity of the external terminals.
German published, non-prosecuted Patent Application DE 36 35 375 A1 discloses the use of a standardized lead frame. In this case, in order to adapt the carrier island to the semiconductor component, a corresponding carrier island is fixed on the central part of the frame.
In order to avoid flexure of a potted element, published European Patent Application EP 0 261 324 A1 discloses arranging the lead frame such that it is centered in height terms in the potting mold in order to ensure that the same amount of plastic reaches above and below the integrated circuit.
Patent Abstracts of Japan Publication No. 60189956 discloses adapting a lead frame configuration having a chip island on which a semiconductor chip is to be disposed to the size of the chip in such a way that the chip island is reduced to the size of the semiconductor chip by removing an edge.
U.S. Pat. No. 4,258,381 describes a lead frame configuration which is intended to be suitable for accommodating different chip sizes. The dimensions to be adhered to for the chip island are specified in this case.